[Grizzley1]

These nipples are metric, You want a 6mm x .75

 

[Grizzley1]

I was going by the dimensions OP gave me, .232 = 6mm, 32 tpi corresponds with a metric .75 pitch.

A 5.5x.9 (.216 diameter) is the Italian translation for the standard machine screw size #12x28.

 

[Grizzley1]

Ok cool. I guess that means the G&U used different nipples from modern Uberti's.

Either that or Navy arms specified that size on guns made for them, they used several manufacturers over the years. Perhaps they wanted all Navy Arms revolvers to have a common nipple size?

 

[Grizzley1]

It's got me a little curious too, I used to have a Uberti Cattleman's Carbine but I never had to pull the nipples on it, so I have no clue what thread size it used.